The present invention relates to a light guiding member, light detecting device and defect inspecting apparatus. More specifically, the present invention relates to a light guiding member which can obtain both functions of a spectral function to separate the light into specular reflection light and diffuse reflection light, or into regular transmission light and diffuse transmission light, and of a light guiding function, by a single member, and to a light detection device using the light guiding member, and a defect inspecting apparatus.
Conventionally, in an optical system of a flying spot system, when a quantity of light at each scanning position is detected, the followings are well known: a light guiding member in which a diffuse reflection band is formed in a direction of a cylindrical axis of a cylindrical light transmission member for light transmission, as described in Japanese Patent Publication No. 39753/1979, Japanese Utility Model Publication No. 43762/1994, etc., and the light entering along the direction of the cylindrical axis is guided to a light detector provided at one end or both ends of the cylindrical light transmission member; and a light detecting device using the light guiding member.
Further, in the optical system of the flying spot system, when the surface inspection of a subject to be inspected is conducted by using the reflected light in which the light scans on the subject to be inspected (irradiated subject) and the light is reflected on the subject to be inspected, or by using the transmitted light in which the light transmits the subject to be inspected, it is well known that information necessary for defect inspection can be obtained more accurately and minutely, by separating the regular transmission light (or specular reflection light) from the diffuse transmission light (or diffuse reflection light), and by detecting a change of each quantity of light.
For example, as described in Japanese Patent Publication Open to Public inspection No. 220636/1984, an example is well known in which the defect inspection is conducted by using a slit mirror. A general view in the case where the defect is detected by using the slit mirror system, is shown in FIG. 1. In this connection, FIG. 1 shows a case in which the transmission light is detected, however, the reflection light can also be used.
An inspection light 1 irradiated from a light source transmits a transparent sheet-like subject to be inspected 2, and becomes 2 types of transmission light of a regular transmission light 4 and a diffuse transmission light 3. The regular transmission light 4 and the diffuse transmission light 3 enter a light receiving portion casing 100; by a slit mirror 5 in the light receiving portion casing 100, the regular transmission light 4 transmits a slit of the slit mirror 5, and a portion of the diffuse transmission light 3 is reflected by a mirror of the slit mirror 5; and thereby, the regular transmission light 4 and the diffuse transmission light 3 are separated from each other into the different directions. Then, the regular transmission light is detected by a regular transmission light detector 11, and a portion of the diffuse transmission light 3 is detected by a diffuse transmission light detector 8. Then, the defect inspection is conducted according to a change of quantity of light respectively detected by the regular transmission light detector 11 and the diffuse transmission light detector 8. In this connection, light detectors have light diffusing plates 6 and 9, and a plurality of photomultiplier tubes (PMT) (not shown). The light, which arrived at respective light detectors, is diffused by the light diffusing plates 6 and 9, made uniform, and then detected by a plurality of PMTs.
Further, another example is also well known in which a diffuse reflection band is formed in the direction of cylindrical axis of a cylindrical light transmission member for light transmission, 3 light guiding members are used in which the light entering along the direction of the cylindrical axis is guided to the light detector provided at one end or both ends of the light transmission member, and thereby, the regular transmission light (or specular reflection light)and the diffuse transmission light(or diffuse reflection light)are separated from each other, and changes of quantities of both light are detected.
In this case, 2 light guiding member are used for light receiving and light guiding of the diffuse transmission light (or diffuse reflection light), and one light guiding member is used for light receiving and light guiding of the regular transmission light (or specular reflection light). Further, a cylindrical lens is provided for converging the diffuse light in the front of the light guiding member for the diffuse transmission light (or diffuse reflection light).
A general view in the case of detection using 3 light guiding members is shown in FIG. 2. FIG. 2 shows the case of detection for reflection light, however, it can also be applied for the detection of the transmission light.
Three light guiding members, that is, the light guiding member 16 for the specular reflection light, and the light guiding members 19A and 19B for the diffuse reflection light are respectively located as shown in FIG. 2.
Detection light 13 is reflected by a sheet-like subject to be inspected 12, and is made to be 2 types of reflection light of specular reflection light 21, and diffuse reflection light 22 and 23. The specular reflection light 21 is received by the light guiding member for the specular reflection light 16. The diffuse reflection light 23 are converged by condenser lenses 20A and 20B for the diffuse reflection light, which are cylindrical lenses, and then, are received by light guiding members 19A and 19b for the diffuse reflection light.
The light guiding member 16 for the specular reflection light and the light guiding members 19A and 19B for the diffuse reflection light are manufactured by forming light scattering bands 15, 17A and 17B, by coating titan oxide particles on the light guiding members 14, 18A and 18B for light transmission.
The light respectively received by the light guiding member 16 for the specular reflection light, and light guiding members 19A and 19B for the diffuse reflection light, is scattered by the light scattering bands 15, 17A and 17B, transmitted through light transmission members 14, 18A and 18B in the direction of the cylindrical axis, guided to light detection means (not shown) located at respective end surfaces of the light guiding member 16 for the specular reflection light, and light guiding members 19A and 19B for the diffuse reflection light, and the defect inspection is conducted according to respective changes of quantities of light detected by the light detecting device by respective light.
However, when the regular transmission light (or specular reflection light) and the diffuse transmission light (or diffuse reflection light) are separated from each other, and the change of quantity of light of both light is detected by using the slit mirror system, there are following problems.
When the slit mirror system is used, because the light is separated into 2 directions of the regular transmission light (or specular reflection light) and the diffuse transmission light (or diffuse reflection light), the size of the casing of light receiving portion becomes large, resulting in the necessity of the large mounting space. Further, a large number of light detection means such as PMT are necessary, resulting in an increase of cost.
Further, in the slit mirror system, a loss of the diffuse transmission light (or diffuse reflection light) is large, (the light which can not enter the casing of light receiving portion, the light which passes the outside of the light diffusing plate 6 after having been reflected by the slit mirror 5, etc.), and only a portion of the diffuse transmission light (or diffuse reflection light) is received and used for the light detection. Accordingly, when the subject to be inspected is photosensitive material such as photographic light sensitive material, a quantity of the light used for the inspection is very small in order to prevent fogging, and as a result, it is necessary to detect a change of the quantity of light of a portion of a very small quantity of the diffuse transmission light (or diffuse reflection light), resulting in much difficulty and inaccuracy.
On the other hand, when 3 cylindrical light guiding members are used, and the regular transmission light (or specular reflection light) and the diffuse transmission light (or diffuse reflection light) are separated from each other, and the change of the quantities of both light are detected, the following problems occur.
At first, 3 light guiding members are used, resulting in a larger light detecting device and a larger mounting space.
Next, the divergence of diffused light becomes larger as the distance from the subject to be inspected becomes larger. Accordingly, in order to receive the diffused light as much as possible by the cylindrical light guiding member, the mounting position of the light guiding member for the diffuse transmission light (or diffuse reflection light)is limited, and therefore, the mounting position of the light detecting device is limited.
Further, when the light scans on the subject to be inspected such as the film-like material or the like, and the reflection light which is reflected by the subject to be inspected, or the transmission light which passes through the subject to be inspected, are used for inspecting the defect on the surface of the subject to be inspected, the diffusiveness of the diffused light is small in many cases. In particular, when the defect of the transparent film-like material or the like is inspected in such a manner that the transmission light obtained when the light scanning on the film passes through the film, is used for inspecting the defect on the surface of the subject to be inspected, the diffusiveness of the diffuse transmission light is small in many cases.
Further, the inventor of the present invention found that the diffused light (near the diverging angle of 2.degree.-5.degree.) near the regular transmission light (or specular reflection light) includes useful information for the defect inspection in many cases.
However, when 3 cylindrical light guiding members are used as shown in FIG. 2, it is physically rather difficult because of small diffusiveness that 3 cylindrical light guiding members are positioned so that the diffused light having small divergence of light and the diffused light near the regular transmission light (or specular reflection light), (for example, numeral 22 in FIG. 2, or the diffused light nearer the regular transmission light (not shown )),can be detected. Accordingly, in order to obtain the diffused light having small divergence of light and the diffused light near the regular transmission light (or specular reflection light), it is necessary to severely set the mounting positions of 3 cylindrical light guiding members.